1. Field of the Invention
The present invention relates to a method for grinding an aluminum substrate and a double-side grinder using the said method. More particularly, the present invention is concerned with the technical field of an aluminum substrate grinding method for grinding an aluminum substrate which, for examples, serves as a magnetic disk to be used as a memory in a computer.
2. Description of the Prior Art
As known well, as to the magnetic disk used in a memory such as a computer for example, the head flying height has been decreased for improving the recording density, and the reduction in size of the disk is also been under way. At the same time, for the disk substrate, not only a further improvement in surface smoothness and morphological accuracy but also the reduction in both thickness and size has been required.
Heretofore, an aluminum substrate has been fabricated by a method involving subjecting a rolled aluminum plate to blanking with a press into a disk shape to form an aluminum substrate, then subjecting the aluminum substrate to annealing for strain removal, thereafter attaching PVA grinding wheels to upper and lower surface plates of a double-side grinder, holding the aluminum substrate in between the upper and lower grinding wheels and grinding it at a low speed. This is because the said method affords an aluminum plate superior characteristics in both surface accuracy and dimensional accuracy.
However, when the aluminum substrate is loaded onto and unloaded from a carrier, it is necessary to interrupt the operation of the double-side grinder used. Thus, a problem remains to be solved such that it is impossible to expect a further improvement in productivity of the aluminum substrate.
To solve the above-mentioned problem, that is, to improve productivity, a study has so far been made about adopting a double-side grinder which grinds double-sides of an aluminum substrate continuously without interruption of operation of the grinder while allowing a disk- or belt-like carrier to pass, together with the aluminum plate, between a pair of grinding wheels rotating at a high speed. Such a double-side grinder is of a known type, but various improvements have been applied thereto for grinding such a soft material as the aluminum substrate. For example, double-side grinders of such a type are disclosed in Japanese Patent Publication Nos. 37378/80 and 304854/94. These double-side grinders will be outlined below.
A description will first be directed to the double-side grinder disclosed in Japanese Patent Publication No. 37378/80 with reference to FIG. 10(a) which illustrates an outline of the grinder and FIG. 10(b) which illustrates a principal portion of the grinder on a larger scale, and using the same designations and reference numerals as those described in the specification thereof.
A belt 53 is stretched between and straddles a driving roll 51 and a driven roll 52 which is positioned a predetermined distance from the driving roll 51. The belt 53 is a metallic belt having pockets 55, the pockets 55 being formed at predetermined intervals and conforming approximately to a small thin piece 54 as a work. Plural such small thin pieces 54 are stacked and are respectively brought into engagement in the pockets 55 by means of an automatic inserting device (not shown) indicated with an arrow 58.
The numeral 59 denotes a guide member disposed above the automatic inserting device 58, while the numeral 60 denotes a guide member disposed in font of the device 58. Numeral 61 denotes a disk-like rotary machining tool, which is provided in a pair and which is disposed sideways of the guide members 59,60 and in parallel with the belt 53. The paired disk-like rotary machining tools 61,61 are constructed so as to be rotated with rotating shafts 62,62. Accordingly, upon counterclockwise rotation of the driving roll 51, double-sides of the small thin piece engaged in each pocket 55 of the belt 53 are ground by the disk-like rotary machining tools 61,61.
Now, a description will be given of the double-side grinder disclosed in Japanese Patent Laid Open No. 304854/94 with reference to FIG. 11 which is a schematic plan view, with an upper grinding wheel omitted. According to this grinder, utilizing a grinding force induced at the time of grinding double-sides of a work W, an outer peripheral surface Wa of the work is pressed against the outer peripheral surfaces as friction surfaces of friction wheels 65 and 66 rotating in positions outside a grinding wheel 67, and the work is rotated forcibly by virtue of the resulting frictional force between the fiction wheels 65,66 and the work W. With this construction, a drive system for driving the work W rotatively can be disposed outside the grinding wheel 67 to grind various works from extremely thin works up to normal works. It is possible to improve the grinding accuracy for works.
Another description will be further directed to a double-side grinder disclosed in Japanese Patent Laid Open No. 18445/95 with reference to FIG. 8 and using the same designations and reference numerals as those described in the specification thereof. A disk-shaped carrier 44 having a plurality of pockets 46 capable of carrying works thereon is rotated between a pair of opposed grinding wheels 42,42, the pockets 46 being formed on a circumference centered at the rotational center of the carrier, to continuously grind double-sides of the works received in the pockets 46 of the carrier 44. Numeral 47 denotes a loading pusher for loading works into the pockets 46, while numeral 48 denotes an unloading pusher for unloading ground works from the pockets 46.
When disk-shaped works are to be ground on double-sides thereof while being carried on or received in the above conventional carrier, if a pair of grinding wheels disposed opposedly to each other are rotated at an equal speed in directions opposite to each other, the forces which the disk-shaped works receive from the grinding wheels during grinding offset each other and become zero theoretically, so that the works are not moved in any direction and hence do not rotate.
Actually, however, the aforesaid forces do not become completely zero due a slight difference in the surface condition between the paired grinding wheels or due to a slight difference in the state of contact between the disk-shaped works and the grinding wheels. In many cases the works undergo a force acting in a certain direction. Particularly, when a disk-shaped work is to leave the paired grinding wheels and when only half or less of the work surface to be ground is being ground with grinding wheels, as shown in FIG. 9 which illustrates in what state grinding marks of each work occur, the work will undergo a follow-up rotation continuously or intermittently with rotation of any one grinding wheel, so that grinding marks extending in a direction different from the previous grinding marks occur on the work surface to be ground. Further, when each disk-shaped work gets in between the paired grinding wheels and when the work leaves the paired grinding wheels, the work rotates due to its follow-up rotation and rubs against an inside wall of the associated pocket in the carrier, resulting in that a peripheral edge of the work is flawed and hence the appearance of the work is deteriorated.
Thus, in the case of grinding double-sides of a disk-shaped work by means of a double-side grinder, it is difficult to avoid the occurrence of grinding marks of different directions or avoid flawing of a work edge. For this reason, for double-side ground products of which it is required to be uniform in grinding marks on double-sides or of which it is required to be flaw-free at an edge, it is impossible to use a double-side grinder for grinding disk-shaped works and therefore the improvement of productivity has been obstructed. Further, the amount of residual stress becomes great, so that not only the resulting disk-like double-side ground product may become wavy but also it is impossible to adopt a double-side grinder for grinding double-sides of a disk-shaped work or which high flatness is required. Thus, the prior art has developed such problems to be solved.